Associative thickeners based on polyurethane belong to the prior art. They are described in detail, for example, in U.S. Pat. Nos. 4,079,028 and in 4,155,892.
The “star-shaped products” (group B) and “complex polymers” (group C) described in U.S. Pat. No. 4,079,028 comprise polyurethanes into which polyhydric alcohols have been polymerized-in. These polyhydric alcohols are low molecular weight compounds such as, for example, trimethylolpropane, pentaerythritol, sorbitol, erythritol, mannitol or dipentaerythritol.
EP 1566393 (Cognis) describes thickeners based on an aqueous preparation of nonionic, water-dispersible or water-soluble polyurethanes which can be prepared by reacting (a) one or more polyfunctional isocyanates with (b) one or more polyetherpolyols, (c) one or more monofunctional alcohols and (d) if desired one or more polyfunctional alcohols, where the compounds (d) comprise no further functional groups apart from the OH groups. The polyfunctional alcohols (d) comprise at least predominantly trifunctional alcohols, such as, for example, glycerol or preferably trimethylolpropane.
EP 1765900 (Cognis) describes thickeners based on an aqueous preparation of nonionic, water-dispersible or water-soluble polyurethanes with a specific structure. The particular structure of these polymers is achieved by the presence of allophanate bonds, which are produced by using an excess of isocyanate. As component (a), it is possible to use hydrophilic polyols with at least 2 OH groups, which may additionally comprise ether groups.
EP 1584331 A1 (Shiseido) describes polyurethane thickeners for cosmetic preparations. The polyurethanes may also be branched. The parent polyols and the alkoxylated derivatives thereof are described in paragraphs [38] and [39].
EP 725097 A1 (Bayer) also describes thickeners based on polyurethanes. Branches can optionally be introduced into the polyurethanes by virtue of component a4). a4) is 3- to 6-hydric alcohols in the molecular weight range 92 to 600, preferably 92 to 400 and particularly preferably 92 to 200, such as, for example, glycerol, trimethylolpropane, pentaerythritol and/or sorbitol. If used at all, preference is given to using glycerol or trimethylolpropane.
EP 978522 (National Starch) describes branched polyurethane thickeners with the following formula(XY1Z)n-A-(ZY2X′)m 
Herein, A is a hydrophilic polyol and preferably selected from trimethylolpropane, [2-ethyl-2-(hydroxymethyl)-1,3-propanediol], pentaerythritol, glycerol and sorbitol.
US 2009/0286940 A1 (DIC Corp.) describes the preparation of hyperbranched polyetherpolyols by ring-opening polymerization of hydroxyalkyl oxetanes and monofunctional epoxides, and also polyurethanes based on these hyperbranched polyetherpolyols.
US 2009/0082483 A1 describes polyurethane foams based on the reaction products of polyisocyanates and polyglycerol, which is hydrophobically modified prior to the urethanization by means of transesterification with naturally occurring polyol esters.
WO 2009/101141 A1 describes a process for the preparation of dendritic polyetherols in which at least one tri- or higher-functional alcohol and optionally further di- and/or monofunctional alcohols and/or modifying reagents are reacted with the help of acidic catalysts. Furthermore, the use of these polyetherols as possible building blocks for the preparation of polyaddition or polycondensation polymers is described.
DE 10211664 A1 describes the synthesis of hyperbranched polyglycerols by ring-opening polymerization of glycidol.